How to rewind Three-Phase induction stator.

How to rewind Three-Phase induction stator.

Introduction:

Three-Phase induction motor or asynchronous motor is a 3 phase AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.

The course consists of the following lessons:

Taking Data, Core  Testing, Coil Cutoff, Burnout Procedures, Winding Stripping Procedures, Core Preparation, Coil Making, Winding Insulation and Coil Insertion, Internal Connections, Lacing and Bracing of Windings, Inspection of Untreated Windings, Testing Untreated and Treated Windings, Winding Treatment.

Tools and equipments; Megger tester, cutter plier, a note book, oven, combination plier, insulators papers.

Lesson 1:

Taking Data, the key objective is to accurately determine winding data for a three phase stator, including connection, turns, span(s), wire sizes, poles, and grouping; and core and coil dimensions. It is important that the new winding data match the original so that the motor produces the same performance characteristics (e.g., horsepower or kilowatt rating and speed) as prior to rewind, and that the energy efficiency rating is maintained. Further, it is important to note that some of the critical data cannot be determined later in the winding process. For example, if the turns are not counted correctly, they cannot be determined after disposing of the removed winding. Using a note book.

Lesson 2:

Core Testing, the main objectives are how to perform a core test using two different methods, and the materials and equipment needed. Another primary objective is recognizing the importance of, and how to evaluate, the results of core testing. A properly performed core test can detect core degradation prior to rewind. To achieve that, the core should be tested before and after the burnout process. The key here is to avoid inserting a new winding into a defective core, then having to repair the core and repeat the rewind process, or worse, having to scrap the stator core. After performing some core tests, the student should have a better understanding of how much time and potential cost can be saved by performing core tests before and after winding removal. Also, by performing the core testing, the student will have a higher level of confidence that the stator core is in satisfactory condition for rewinding. Using a megger tester

Lesson 3:

The critical objective of the Coil Cut-off lesson is to be able to cut off coil extensions without injury to the technician or the stator. Essentially the idea is to cut the copper wire, not any other metal part of the stator, and to do it in a manner that does not harm the stator or the person performing the task. Proper cutting of the coil extensions also reduces time and effort when pulling the coils out. Using a cutter plier.

Lesson 4:

Following the cutting off of the coils, the next step is Burnout. Important objectives of the lesson on the Burnout process are to understand how the burnout oven works in a temperature-controlled manner, and how to operate and properly load the oven. The burnout oven breaks down the winding insulation, to facilitate winding removal. A key aspect of the burnout process is for the student to recognize that control of the part temperature is much more critical to the process than simply controlling chamber temperature.

Lesson 5:

The next step in the rewind process is Winding Stripping. Primary objectives in this lesson are understanding and using winding removal methods and equipment to remove the old winding safely, and avoiding damage to the stator core. Because stripping methods and equipment vary, the mentor should provide the student with specific instructions on winding stripping in their service center. Closely associated with Winding Stripping is Taking Data, as much of the important data is obtained during the stripping process, e.g., connection, turns, span(s), wire sizes, poles, and grouping. Note that this is a return to the data taking lesson that began the winding process. Using combination plier.

Lesson 6:

After removal of the windings and insulation, the bare core must be made ready for winding insertion. Key objectives in Core Preparation are how to clean, inspect and prepare the bare core; and how to repair lamination damage and defects. This step assures that the core is in satisfactory condition prior to actual rewinding, and is associated with the Core Testing lesson. The prepared core is core tested to verify that core losses have not increased from the initial core test by an unacceptable amount.

Lesson 7:

All of the steps and associated lessons to this point have dealt with existing windings and stator components. The first step in actual rewinding is Coil Making; that is, creating new coils from new magnet wire and other materials. The primary objectives of Coil Making are recognizing the materials, tools and equipment needed; and how to make random wound coils to be installed into a three-phase stator core.

Lesson 8:

Having made new coils, they need to be inserted into the core, bringing up the next step, Winding Insulation and Coil Insertion. The objectives of this lesson are to be able to determine the materials and tools needed; and how to install random-wound coils into a three-phase stator core. There are actually multiple steps in this process, dealing with insulating and inserting. The slots are insulated, then coils inserted, followed by insulating between coils

Lesson 9:

Even though the winding coils have been made and inserted correctly, the winding will not perform properly if it is not connected correctly. This is accomplished in the next step, Internal Connections. In addition to requiring physical accuracy and attention to detail, the student will learn the steps necessary to “lay out” and verify the accuracy of the connection. Critical objectives of this lesson are how to identify and lay out winding connections, and the procedures for actually connecting the winding

Lesson 10:

The inserted winding coils should be snug in the slots, but will need reinforcement to reduce the tendency to move or shift. Varnish treatment and curing will do much to make the winding more rigid; however, there is another key step to be used to reinforce winding coils. That is Lacing and Bracing of Windings, with the main objectives being to make the winder proficient in the methods, materials and procedures for lacing and bracing of windings.

Lesson 11:

The next action step for the winding is to treat and cure it. This step is essentially irreversible. That is, the treated winding cannot easily be modified if, for example, the connection is incorrect or there is a ground fault. Therefore the next steps in the winding sequence are to inspect and to test the untreated winding. The primary objective of Inspection of Untreated Windings is how to properly inspect and evaluate an inserted and untreated three-phase random winding for defects or imperfections.

Lesson 12:

Following inspection the companion critical objectives of Testing of Untreated and Treated Windings are how to perform and evaluate testing of untreated, and of treated, three-phase random windings. The student receives information on the applicable tests, how to perform them, and how to evaluate the results.

Lesson 13:

Following inspection and testing of the untreated winding we move on to the final step in the winding process, Winding Treatment. This step is crucial to providing a winding with good heat transfer, high bond strength, and protection against contamination. The key objectives of Winding Treatment are to make the winder knowledgeable and proficient in the equipment and materials to varnish treat and cure windings; and the methods and procedures to varnish treat, cure and evaluate the finished three-phase random winding. The actual final step is testing the treated winding, described above.